1. Field of the Invention
This invention relates to a novel process for the oxidation of methane and a wide range of hydrocarbons in the liquid phase in the presence of air or oxygen catalyzed by complexes of ruthenium activated by the presence of an end-or bridged oxo group along with carboxylato groups. This process provides a high yield with good catalytic turnover efficiency.
2. Background of the Invention
The oxidation of alkanes such as methane, ethane, propane, butane and the like can be difficult to achieve. Methane can be especially difficult to oxidize. Many methods have been developed to oxidize methane and other hydrocarbons. However, these methods generally produce very low yields of oxidation product and utilize expensive catalysts which must be replenished frequently. The use of metalloporphyrin catalysts such as Fe(TPP)C1 and Mn(TPP)C1 (where TPP=the dianion of 5,10,15,20-tetraphenylporphine) with iodosyl benzene, sodium hypochlorite and alkyl hydroperoxides or other costly nonregenerative oxidants has been reported. [P. Traylor, D. Dolphin and T. Traylor, J. Chem. Soc. Chem. Comm., 279 (1984), J. Groves, W. Kruper, Jr., R. Hanshalter, J. Am. Chem. Soc. 102, 6377 (1980), J. Smegal and C. Hill, Ibid, 105, 3515 (1983).] Oxidation of a variety of hydrocarbons other than methane has been achieved by the use of the binuclear Fe(III)-.mu.-oxo-.mu.-acetate complexes in the presence of the oxidant, t-butyl hydroperoxide and O.sub.2. [J. B. Vincent, J. C. Huffman, Chiston, Q.Li, M. A. Nancy, D. N. Hendrickson, R. H. Fong, R. H. Fish. Ibid, 110, 6898 (1988)]. [C. Chin and D. T. Sawyer, Ibid 112, 8212 (1988)]. These methods are expensive and the reagents are nonregenerative.
Azide-activated complexes of several metals in the presence of ligands such as TPP, and acetylacetonates and air or molecular oxygen have been used to catalyze the oxidation of isobutane, propane and cyclohexane at 70.degree.-180.degree. C. and 20-170 atmospheres in the liquid phase. The catalysts are inactive in the absence of the azide. [U.S. Pat. Nos., 4,895,680 and 4,895,682].
Heteropoly acids with site specific framework have also been used for the oxidation of alkanes in the liquid phase in the presence of oxygen at 125.degree.-175.degree. C. and 170 atmospheres. With such a method propane can be oxidized to acetone and isopropyl alcohol [U.S. Pat. Nos., 5,091,354 and 4,898,989]. Cyano-substituted and nitro-substituted metalloporphyrins have been used for the oxidation of isobutane to isobutyl alcohol at 70.degree.-180.degree. C. and about 25 atmosphere of pressure.
In these systems, the ligands are costly compounds and the recyclability of the catalysts remains questionable. In addition, although methane is included in the general list of hydrocarbons that can be oxidized, the oxidation of methane is not specifically discussed or illustrated. [U.S. Pat. Nos., 5,118,886 and 5,120,882].
The gas phase oxidation of natural gas to methanol by molecular oxygen in the gas phase has been disclosed by Walker et al. [U.S. Pat. No. 2,007,116] and by Gesser et al. [U.S. Pat. No. 4,618,732]. In the latter case, a 13% conversion of natural gas (composition not mentioned) was claimed at 300.degree.-500.degree. C. and 10-100 atmospheres. V. A. Durante et al. [U.S. Pat. Nos. 4,918,249 and 5132472] used silicometallates as catalysts for the gas phase oxidation of methane to methanol at 300.degree.-600.degree. C. and 10-70 atmospheres. A 7% conversion of methane to the oxidation products methanol and CO.sub.2 was reported. With a reaction column filled with sand or inert refractory inorganic particles, Scott Hans [U.S. Pat. No. 4,982,023] disclosed a 5.5% conversion of methane to methanol at 300.degree.-500.degree. C. and 10-100 atmospheres. With a ZSM-5 packing, a direct conversion of methane to aromatics was reported at 300.degree.-500.degree. C. and 5-100 atmospheres [U.S. Pat. No. 5,012,029].
It is therefore to be noted that except for the gas phase oxidation of methane to methanol, which involves large energy inputs and low yields, a truly catalytic low energy liquid phase oxidation of methane to methanol has not yet been achieved.
It is therefore an object of this invention to provide a truly catalytic process for the oxidation of methane and other hydrocarbons to alcohols, ketones and other such products, which uses air or oxygen, and a metal coordination complex as a catalyst, and which requires low energy input, produces high conversion rates and has high product efficiency.
Another object of this invention is to provide a process for oxidation of methane and other hydrocarbons where a truly catalytic cycle is achieved with the active catalyst having a high turnover efficiency.
A further object is to provide a process for oxidation of methane and other hydrocarbons where there is no need for the addition of expensive compounds to regenerate the catalyst or for the use of non-regenerable oxidants.